1. Field of the Invention
The present invention relates to a cellulose acylate film and a method of producing thereof.
2. Description Related to the Prior Art
A cellulose acylate film formed of cellulose acylate is used as a base of a photosensitive material, as cellulose acylate is strong and has incombustibility. In the cellulose acylate film there is for example cellulose acetate. Recently, cellulose acetate having an acetylic degree between 57.5 and 62.5% becomes preferable to be used as a protective film of a deflective plate and a color filter in a liquid crystal displaying device, while having an extremely optical isotropy.
The cellulose acylate film is usually formed in a producing method of a film from a solution. In the producing method, the cellulose acylate film may be produced so as to have better optical character and properties of matter than in melt-casting method and the like. In the producing method, the cellulose acylate is solved in a solvent to obtain the solution. The solution is applied on a dope band, and thereafter the solvent is evaporated to form the cellulose acylate film. As the solvent, hydrocarbone halides (especially methylene chloride and the like) and are used.
However, when containing the solvent so much, the solvent evaporates suddenly. Therefore, bubbles issue in the dope solution in a high temperature, which makes the quality of the cellulose acetate film lower.
Further, when the solvent is evaporated from the cellulose acetate film entirely, the cellulose acetate film loses a flexibility and becomes to be easily broken and cut. Further, when the solvent remains in the cellulose acetate film so much, a thermal shrinkage of the cellulose acetate film issues easily to make a quality thereof lower. When the cellulose acetate film with the thermal shrinkage is used as the protective film of the deflective plate, the deflective plate is deformed. Accordingly, phases close to edges on the deflective plate becomes disordered, and images thereon are deformed.
The thermal shrinkage of the cellulose acetate film is not entirely prevented, as the temperature changes in producing the cellulose acetate film. So as to compensate for the deformation of the cellulose acetate film, a pressure sensitive may be used. However, as the pressure sensitive is heavily hardened, it flows out on a surface through which the deflective plate is cut. Accordingly, when the cellulose acetate film is used as the protective film, it should be transparent and low complex reflactive, and stability to the change of the temperature.
Recently, it becomes problematic because of circumstance protection to use the hydrocarbon halides (for example, methylene chloride), and it is requested to reduce the amount of hydrocarbon halides to be used. Accordingly, methylacetate, ketones and the like are used as the solvent, and the cellulose acylate is solved in them in an especially low temperature or a high temperature, or a large pressure is applied during solving the cellulose acylate.
Also when the ketones are used as the solvent, the ketones should not remain in the cellulose acetate film so much. When cellulose acetate film containing so much ketones, the ketones change the color of the deflective elements in the deflective plate such that the deflective plate becomes unusable.
Further, when components generated by dissolving of the cellulose acylate remains in the cellulose acetate film, the cellulose acylate film accelerates the transesterification and the dissolution of the cellulose acylate film. Thus, carboxylic acid is produced (especially acetylic acid is produced when methyl acetate is used as cellulose acylate). Accordingly, when the cellulose acylate film is used in the deflective plate, the deflective plate may be easily deformed in large temperature and humidity.
Note that it is proposed to use a cycloester as the solvent. In this case, however, the cycloester is hardly used as it has large inflammability and dissolutes easily.
An object of the present invention is to provide a cellulose acylate film in which thermal shrinkage does not issue so much.
Another object of the present invention is to provide a cellulose acylate film in which a solvent remains at a predetermined weight percentage.
Still another object of the present invention is to provide a cellulose acylate film produced without harmful influences on a circumstance.
In order to achieve the object and the other object, the cellulose acylate film contains the solvent at 0.1-0.6 wt. %. The solvent is composed of at least one of esters and ketones. Further, the cellulose acylate film contains acids at 500 ppm that are products of dissolution of the esters. Furthermore, the solvent may contain a recycled solvent at 80% before producing the cellulose acylate film. The recycled solvent is recycled during production of the cellulose acylate film.
In order to produce the cellulose acylate films, a support (or dope band) is moved, on which the solution is applied. In the solution, an amount ratio of the solvent is 10-200 wt. % to cellulose acylate. The solution is dried on the support to form a film-like material. The film-like material contains the solvent at less than 200 wt. %, preferably less than 10 wt. %, to the cellulose acylate, and is peeled from the support. Then the film-like material is dried to form the cellulose acylate film containing the solvent at between 0.1-0.6%.
According to the cellulose acylate film of the present invention, the thermal shrinkage does not occur so much. Further, the producing of the cellulose acylate film does not harmfully influence on the circumstance so much.